Screen Video Recording Overview
When you record a screen movie using Screen Recorder Gold, you are actually saving a sequence of bitmaps (known as frames), that, when displayed in rapid succession, exhibit motion.
If more frames are recorded per second, the resultant animation will also be smoother. However, this will also cause the file size of the movie to be much larger and will consume more CPU time.
In the process of recording, Screen Recorder Gold allows you to specify two video rates: the capture rate and playback rate. The capture rate tells your computer how many frames to record per second. The playback rate tells your computer how fast to play them back. Usually, these two rates are equal, so that the time of playback is equal to the time used in the recording.
However, these two rates can also be different. Normally, you do this only if you want to create a time-lapse movie. For example, you can capture a frame once every hour and play the frames back at 20 frames per second.
There is also a third rate: known as the keyframe rate. When a frame is saved in an AVI file, they can either be saved as a full frame, or only as a difference to the previous frame. This keyframe rate specifies how often full frames are written to the AVI file. A high value means you can fast forward/rewind to a particular frame in your movie much faster. But it also means a larger file size.
The video data in an AVI file can be formatted and compressed in a variety of ways. Once you understand the concept of compression, everything else is easy so we're going to take a minute to explain in semi-technical terms. Before we begin please note that compressing a movie file is also called encoding so either word may be used indiscriminately.
- Intel Indeo (version 3.2)
- Microsoft Video 1
- Microsoft RLE (Run Length Encoding)
AVI is not restricted to these compressors. They are the compressors provided with your operating system. You an install other codecs on your system.
The MOST COMMON reason that a video file will not play is that the video codec (compressor/decompressor) used by the file is not installed on the system being used to attempt to play the file. Usually, the Windows operating system, Windows Media Player, or the application that you are using will report an error indicating that the codec is not present or that it cannot find the codec needed. Each video codec is identified by a four character code such as IV50 or DVSD.
Lossless/Lossy compress and video Quality
Some codecs use lossless compression, which ensures that all of the information in the original clip is preserved after compression. This maintains the full quality of the original, which makes lossless compression useful for final-cut editing or moving clips between systems. However, preserving the original level of quality limits the degree to which you can lower the data rate and file size, and the resulting data rate may be too high for smooth playback on many systems.
Lossy compression methods discard some of the original data during compression. For example, if the pixels making up a sky actually contain 78 shades of blue, a lossy codec set for less-than-best quality may record 60 shades of blue. Lossy codecs usually let you specify how much picture Quality you want to trade to lower the data rate and file size so that you can tailor playback for your audience. Lossy compression allows much lower data rates and file sizes than lossless compression, so lossy codecs are commonly used for final production of video delivered using CD-ROM or the Internet.